I believe that part of painting is an exercise in imagery and imagination. A painting topic may come from a dream, a past experience, or a subtle non-verbal expression of an experience. The best part of painting though is definitely the imagination aspect. You can create any kind of reality you want, not even bound by dimension even though you are painting on a canvas.

I've done a couple paintings on five side canvases that I stretched up myself. It's more challenging to stretch the canvas over the edges, but it is possible!